This invention relates to processing of hydrocarbon streams in a petroleum refinery, and more particularly to production of a high octane motor fuel.
Many petroleum refineries utilize a delayed coking unit to process residual oils. In delayed coking, overhead vapors from the coking drum pass to a fractionator where various fractions are separated. One of the fractions is a gasoline boiling range stream. This stream, commonly referred to as coker gasoline, is generally a relatively low octane stream, unsuitable for use as an automotive fuel without upgrading. With the limitations on octane improving additives imposed by environmental concerns, it has become desirable to process coker gasoline in an octane improving unit such as a catalytic reformer. Sulfur compounds in coker gasoline are detrimental to catalytic reforming catalysts, and accordingly it has become commonplace to treat coker gasoline in a catalytic desulfurizer prior to processing it in a catalytic reformer. The above discussed steps of delayed coking, desulfurization and reforming are well developed commercial processes which are widely used in the refining industry, and do not constitute a part of this invention.
In the delayed coking process, quantities of foam are often produced which are undesirable as the foam diminishes the efficiency of the delayed coking process. It is customary, as described in U.S. Pat. No. 3,700,587, to add silicone defoamers, for example polydimethyl siloxanes, to delayed cokers to control the undesirable foaming. These defoamers result in an undesirable level of organic silicon in the coker gasoline fractionated from the coker overhead vapors. It is believed that the organic silicon compounds inactivate the catalyst used for desulfurization of the coker gasoline, such that it is desirable to remove the organic silicon compounds from coker gasoline prior to contacting a catalytic material with the contaminated coker gasoline.
The use of activated alumina and related materials to treat hydrocarbon streams is described in U.S. Pat. Nos. 2,403,088; 2,413,868 and 2,890,257. U.S. Pat. Nos. 3,919,077 and 3,954,603 describe the use of guard beds of material to remove catalyst poisoning contaminants from hydrocarbon streams. However, none of the above-noted references are directed to the problem of removal of organic silicon from coker gasoline prior to upgrading of the coker gasoline by a catalytic operation.